This invention relates to a rocker-type switch commonly known as a single pole double throw switch, and more particularly to an improved construction for a center contact arrangement and a movable contact member for use in such a switch.
A single pole double throw (SPDT) switch typically includes a housing within which first and second stationary contacts are mounted, and a stationary center contact is located between the stationary first and second contacts. A movable contact member or rocker is located within the housing, and selectively connects the center contact to either the first stationary contact or the second stationary contact, in response to operation of an actuator movably mounted to the housing.
The stationary center contact is generally in the form of a xe2x80x9csaddlexe2x80x9d member on which the movable contact member pivots for movement between its first and second operative positions. The xe2x80x9csaddlexe2x80x9d construction of the center contact is formed by a generally U-shaped member formed of a conductive material such as copper or brass. The movable contact member is generally V-shaped, defining a central area which engages the edges of the U-shaped center contact. With this construction, the movable contact member moves between the spaced apart edges of the center contact when the movable contact member is moved between its first and second operative positions. This can result in arcing between the edge of the stationary center contact and the facing area of the movable contact member, which causes surface irregularities and resistances which can ultimately result in overheating of the switch.
It is an object of the present invention to overcome the shortcomings of the prior art by providing an electrical switch which maintains constant contact between the movable contact member and the stationary center contact as the movable contact member is moved between first and second operative positions. It is a further object of the invention to provide such an electrical switch which requires relatively minor modifications to prior art switch constructions, while avoiding drawbacks associated therewith. It is a further object of the invention to provide such an electrical switch having a movable contact member that maintains positive contact with the center contact arrangement, without oxidization. Yet another object of the invention is to provide such an electrical switch which includes a unique geometric relationship between the stationary center contact and the stationary first and second contacts, to facilitate movement of the movable contact member between its first and second operative positions and to ensure positive contact of the movable contact member with the stationary center contact and the stationary first and second contacts.
In accordance with the invention, an electrical switch generally includes a housing including a base defining an internal cavity, in combination with a cover engageable with the base and an actuator movably mounted to the cover. A stationary center contact is secured to a lower wall defined by the base, and spaced apart stationary first and second contacts are secured to the lower wall of the base on opposite sides of the stationary center contact.
The stationary center contact defines an upwardly facing substantially planar contact surface, and the stationary first and second contacts also define upwardly facing substantially planar contact surfaces. The contact surfaces of the stationary first and second contacts are disposed below the plane of the upwardly facing contact surface of the stationary center contact. The movable contact member is in the form of a V-shaped member having first and second arms extending outwardly from a common center or vertex. Each of the first and second arms has a contact member secured toward its outer end. The movable contact member of the first arm defines a thickness, and includes a downwardly facing contact surface which is selectively engageable with the upwardly facing contact surface of the stationary first contact. Similarly, a movable contact member is mounted toward the opposite end of the second arm, and includes a downwardly facing contact surface which is selectively engageable with the upwardly facing contact surface of the stationary second contact. The movable second contact defines a thickness equal to that of the movable first contact. The thickness of the first and second movable contacts is substantially equal to the difference in elevation between the contact surface of the stationary center contact and the contact surfaces of the stationary first and second contacts. In this manner, the first and second contact arms extend perpendicularly to a longitudinal axis defined by the switch housing, when the movable contact member is in the first and second operative positions, respectively.
To facilitate conductive contact between the movable contact member and the contact surface of the stationary center contact, at least the portion of the movable contact member that engages the contact surface of the stationary center contact is coated with a conductive coating, such as silver. In this manner, oxidization of the center contact area of the movable contact member is prevented, to ensure conductive contact between the stationary center contact and the movable contact member.
The actuator is preferably in the form of an actuator member pivotably mounted to the housing, which includes a plunger member engaged with the movable contact member for moving the movable contact member between its first and second operative positions in response to pivoting movement of the actuator member. The plunger member is biased outwardly into contact with the movable contact member, to press the center contact area of the movable contact member into engagement with the upwardly facing contact surface of the stationary center contact. The biased plunger further acts to press the movable first and second contact members into engagement with the stationary first and second contacts, respectively, when the movable contact member is in the respective first and second operative positions.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.